Pregnant women are full of questions about their pregnancy, their bodies, and their babies. One of the most stressful questions for late term women is am I having contractions? Answering this question is key to understand when labor is starting, allowing a pregnant couple to prepare for the imminent delivery and eventually leave, in a timely manner, for the hospital or the care institution where the delivery will happen. During the second and third trimester already, women may experience early contractions, also referred as Braxton Hicks contractions. Braxton Hicks contractions are the manifestation that the uterus is slowly preparing for the delivery. The feeling of a contraction is completely new and it is impossible for a woman to reliably identify a contraction from other abdominal physiological disturbances such as abdominal cramps or bowel disturbances. This is especially true for first time moms, but second and third time moms also report this problem, as they would often forget what a contraction feels like.
Next to pregnant women, clinicians have a vast interest in monitoring contractions. History of contractions is part of the clinical examination in most countries, and an OBGYN will typically ask her pregnant patient whether she has had contractions since her last visit, and how often. The answer to this question is inevitably inaccurate since a woman is not able to reliably report contractions.
Despite the importance of monitoring contractions outside the hospital or physician's office, from both a consumer and clinician perspective, there is to date no solution available for contraction monitoring outside controlled clinical settings. The best alternative solution available today for consumers is a stopwatch, physical and digital. Stopwatches rely on the woman's perception and feeling of a contraction, and are therefore intrinsically inaccurate and do not address the problem that woman cannot recognize or detect their contractions.
In healthcare practices, contractions are measured using a tocograph, which measures the pressure resulting from the contraction using a probe positioned on the woman's abdomen. The tocograph has several limitations. First, a tocograph is obtrusive, as it requires a woman to use a strap around her abdomen, a large pressure probe and gel. The obtrusiveness of a tocograph limits its applicability outside controlled clinical environments. Second, the position of the tocograph probes is important in getting a reliable measurement. As a consequence, the tocograph has to be operated by trained clinical staff and cannot be used by the pregnant woman herself. Third, a tocograph only measures the result of the contraction (a change in pressure on the surface of the abdomen), and not the actual physiological phenomena leading to the contraction. As a consequence, tocographs have shown low accuracy in characterizing contractions, especially the intensity of the contractions.
Physiologically, the contraction originates with the electrical activation of uterine cells, similar to the activation of muscle cells. Measuring the uterine electrical activity is a more accurate and more reliable way of measuring contractions called electrohysterography (EHG). US2012/0150010-A1 describes a device and method for monitoring uterine activity based on EHG. However, such devices are today limited to bulky devices with electrodes and wires, operated by clinically experienced staff, and limited to the clinical environment. Attempts have already been made to improve the ease of use and the bulkiness of such devices. US2007/0255184-A1 discloses a disposable labor detection patch using electromyogram signals of the uterus. However, such a concept of a disposable patch integrating all the electronics will inevitably be associated with a very high cost due to the cost of the electronic components, hindering is practicality and usability as a disposable system. Although the electrode part of the system needs to be often replaced for hygiene and signal quality reasons, the electronics can be used for hundreds or thousands of recordings without the need to be dispose or replace it. Furthermore, although a patch may be applicable for some pregnant women, attaching an adhesive on the abdomen of a pregnant women often will be considered uncomfortable as it may lead to itching sensations, irritations, allergies or other disturbances. For such cases, considering other form factors than a patch would be advantageous.
Furthermore, the devices of US2012/0150010-A1 and US2007/0255184-A1 are limited in their functionality. These devices merely provide a measurement of the contraction signal, and do not perform any further analysis on the signal. As a result they are of limited value to the user directly, but require the intervention of a clinically experienced staff to interpret the results.
Electrodes placed on the abdomen of a pregnant woman are capable of measuring bio-potential signals that comprise various electrical signals generated by the body such as the maternal electro-cardiogram (mECG), the fetal electro-cardiogram (fECG) as well as the uterine electrohysterogram (EHG) and uterine electromyogram (UEMG) which is equivalent to the electrical signature of the uterine muscle contraction. The electrohysterogram can be seen as a high level view on the uterine electrical activity, looking at the slower waves that are generated by the common activation of a larger number of uterine cells. Complementarily, the uterine electromyogram can be seen as a fine view on the uterine electrical activity, looking at the fast paced electrical waves generated locally by smaller sets of uterine cells. EHG signals are usually analyzed in the time domain, using RMS, linear filters or other statistics, to come to an estimation of a contraction signal. UEMG signals are usually analyzed in the time frequency domain using Fourier transforms, wavelet transforms, etc. EHG and UEMG signals are superposed to the maternal and fetal electro-cardiogram. Signal processing techniques are also required to isolate every physiological contributions to the bio-potential signals.
All these signals are monitored during long periods of time in the hospital during labor or in the last months of the pregnancy for monitoring and need to be further analyzed by a care specialist. These signals are usually displayed on a screen or printed on a sheet of paper while the signals are being recorded.
In view of the foregoing, a need exists in pregnancy monitoring for a device and a method for contraction monitoring that can be used by pregnant women in any environment, answering the most stressful questions that women have as they are progressing throughout pregnancy, while providing important clinical information that the healthcare practitioner can use during his clinical examination.